A conventional laser printer has a main casing, and, within the main casing, a process cartridge retaining a photosensitive drum and a developing roller is detachably mounted. A toner cartridge in which toner is accommodated is mounted in the process cartridge.
The photosensitive drum and the developing roller are disposed in the process cartridge such that a circumferential surface of the photosensitive drum is in contact with a circumferential surface of the developing roller. The process cartridge has a curved partitioning wall at a position opposite the photosensitive drum relative to the developing roller. The partitioning wall is formed so as to conform to an outer shape of the toner cartridge. The process cartridge is further provided with a cartridge accommodating portion for accommodating the toner cartridge at a position opposite the photosensitive drum and the developing roller relative to the partitioning wall. The cartridge accommodating portion includes a shutter movable along the partitioning wall. The partitioning wall is formed with frame-side passing ports penetrating the partitioning wall. The partitioning wall has a surface confronting the shutter, and annular frame seals are affixed to the surface. Each annular frame seal encircles a perimeter of the frame-side passing port.
The toner cartridge includes an inner casing for accommodating toner and an outer casing for movably accommodating the inner casing. The inner casing has a circumferential wall formed with inner-casing passing ports. The inner casing has an outer circumferential surface provided with toner seals so that each toner seal encircles a perimeter of the inner-casing passing port. The outer casing has a circumferential wall formed with outer-casing passing ports at positions corresponding to the inner-casing passing ports. When an inner circumferential surface of the outer casing confronts the inner-casing passing ports, the inner-casing passing ports are closed by the outer casing.
When the toner cartridge is mounted in the cartridge accommodating portion, the toner cartridge is moved downward toward the cartridge accommodating portion while the inner-casing passing ports are closed by the outer casing. When the toner cartridge has been accommodated in the cartridge accommodating portion, the toner cartridge is pressed toward the partitioning wall. Then, the shutter and the inner casing are integrally moved, so that the inner-casing passing ports are brought into confrontation with the frame-side passing ports through the outer-casing passing ports. Hence, a space in which the developing roller is accommodated communicates with the interior of the toner cartridge (the interior of the inner casing) while the inner casing and the outer casing are sealed by the toner seals and the outer casing and the partitioning wall are sealed by the frame seals.